The present invention concerns a chimney-pipe, a process for manufacturing a cylindrical or tubular moulding body of plastic, in particular chimney-pipes, furthermore a device particularly for carrying out the manufacturing process, as well as a use of the plastic material PET.
For about 10 years, the applicant has developed and sold plastic chimneys with high success, realized with the material PVDF. This tough and high temperature resistant material note only reaches the critical limit of 160xc2x0 C. for exhaust temperatures, also, this material is sufficiently resistant to condensate, and is classified in fire-protection class V0.
As a result, such a plastic chimney has been established as a serious alternative to traditional chimney-pipes from stainless steel.
A disadvantage of such known plastic pipes, however, are the high manufacturing costs due to the expensive material and the critical manufacturing process; compared to stainless steel pipes, therefore, a PVDF chimney-pipe is competitive only to a limit extent.
Certain attempts have been made to find alternative plastic materials, as an example, PP or other thermal plastic materials have been used as input materials. Particularly for the intended, demanding application in the field of chimneys, however, such products have not proven sufficiently temperature resistant, nor up to the further requirements.
From Patent Abstracts of Japan, Vol. 012, No. 186 (C-500), 31.05.1998 (Publication No. 62290750) a tubular gas pipe is known produced as a moulding body of a PET plastic material which is present in crystalline state.
Furthermore, from CH-A-686 082 a moulding body of plastic is known which has been produced from a starting material showing PET pieces of crushed PET bottles.
Finally, from U.S. Pat. No. 4,526,831 the use of a PET-based plastic material in crystalline state is known for the production of car body parts, wheel rims and other elements related to the construction of vehicles.
The present invention has been developed with an aim of providing a chimney-pipe which, contrary to the common-type PVDF chimney-pipe, can be manufactured in an easier way, needs less expensive raw material and, with regard to its mechanical and physical properties, achieves at least the same efficiency as the latter one. Furthermore, a manufacturing process is to be provided for a chimney-pipe of this type as well as a device for the production of the same, and further fields of application have to be found for the material to be provided for according to this arm.
Advantageously, the used crystalline PET which has been produced according to the invention, offers exceptional mechanical properties and in particular can excellently cope with the ambient conditions prevailing within a chimney; moreover, PET as a raw material, from drinking bottles, for example, is available in large quantities and until now there has not been provided an appropriate process for using this recycled raw material.
Essential for the invention is the fact that the chimney-pipe contains the PET material (polyethylene terephthalate, also abbreviated as PETP) in crystalline state. While the plastic bottles which are referred to as initial products contain PETP in amorphous, transparent state, it is necessary to bring the PET into the crystalline state in order to achieve the desired and, according to the invention, advantageous high mechanical stability, toughness and temperature resistance; according to the invention this is achieved in particular by slowly cooling down the manufactured workpiece (contrary to that, in mass production PET bottles are manufactured by injection moulding and blowing as injection-molded parts, and after stretching, by supplying air, they are formed in a cooled and cold mould so that amorphous, transparentxe2x80x94and softxe2x80x94material is produced).
In particular, (PET) material is also considered as being xe2x80x9ccrystallinexe2x80x9d in the sense of the present invention if it does not show a complete but rather partial crystalline state. Such a partial crystalline state is also to be regarded as xe2x80x9ccrystallinexe2x80x9d in the sense of the present invention as soon as, contrary to the amorphous state, advantageous strength properties can be achieved.
Essential for the invention is also the transparent PET produced by cooling down in a direct recycling process without the production of granulate, for applications without thermal load, such as cable conduits, drainage pipes or chimney-pipes for the most advanced condensing value boilers, with these heating installations exhaust gas temperatures of below 100xc2x0 C. leading to a thermal load of max. 40 to 50xc2x0 C. Amorphous PET can be produced at a considerably higher production speed, such as 10-20 m/min. Additional heat retention is not necessary and the productions costs of these simple, thin pipes are reduced by more than 60%.
Moreover, the present invention solves one of the main problems which until now have been preventing commercial processing or reutilization of recycled PET material: PET is hygroscopic and absorbs about 0.5% water from the air. This content of moisture is a main problem in processing and it is the reason why PET, until now, has been used industrially as an original material for composite fiber material (xe2x80x9cTreviraxe2x80x9d of the Hoechst company) and for the above-mentioned drinking bottles only; processing of PET which has not been dried separately and which possibly contains even trace amounts of moisture, therefore, leads to a chemical reaction referred to as thermal hydrolysis which completely destroys the polymer chains of the PET material and converts the polymeric substance into an unusable, highly liquid, monomeric mass of low viscosity. Therefore, until now processing of PET, for example as a granulate, has only been possible after time-consuming and expensive pre-drying and by keeping it dry in the packing until use. Particularly for simple, inexpensive and flexible processing, however, this material has not been available until now, all the less for manufacturing mechanically tough and resistant moulding bodies.
Any plastic body can be regarded as a moulding body in the sense of the invention, which can be manufactured by means of an appropriate plastic moulding process, such as most preferably extruding, injection moulding and blow moulding processes.
Moreover, the invention also comprises the manufacture of sectional or rod elements which are not manufactured in the form of a tube but which can equally make use of the particular, advantageous mechanical effects of the used crystalline PET material.
Independent protection in the scope of the invention is claimed for the use as plastic pipe, in particular as a chimney-pipe which has been manufactured by using the PET material and in this connection it is not decisive that this material is present in a crystalline state. According to the invention it is rather claimed that the pipe is manufactured by the use of crushed PET bottles, by subsequently kneading and allowing the residual moisture to escape in the form of vapour.
This aspect of the invention allows the use of even amorphous PET materials, which have been produced by cooling down in a direct recycling process, without the production of granulate, for applications without high thermal load, such as cable conduits, drainage pipes or chimney-pipes for the most advanced condensing value boilers with exhaust gas temperatures of below 100xc2x0 C. leading to a thermal load of max. about 40 to 50xc2x0 C. Amorphous PET used according to the invention, for example, can be used at considerably higher production speed, such as 10 to 20 m/min in the case of pipe manufacturing. In addition to that, by avoiding the slow cooling down which, for example, would be necessary to obtain the crystalline state, the manufacturing process is considerably simplyfied thus leading to an increase in efficiency of up to about 60% as, for example, in the case of simple pipes.
Additional independent protection is claimed for a use of the crystalline PET produced in the aforementioned way, for applications in the building, water or electronic sectors, as for example downpipes, gutters or the like, as well as cable conduits. Besides, for the material to be produced according to the invention typical fields of application would be window frames or window sections (the crystalline PET would be a particularly inexpensive substitute for rigid PVC) as well as roof tiles or the like coverings.
An additional field of application would be the construction of vehicles or automotive engineering. The tough, resistant crystalline PET material would be particularly suitable for car body parts, such as mudguards or doors, as well as for wheel rims and the like components which are subjected to mechanical stress and have been primarily manufactured of sheet steel or aluminium until now.
A further field of application which is claimed in the scope of the invention would be the sports and recreational sectors; the resistant, tough PET material in crystalline state, for example, could be suitable for the production of bearings for roller blades or the like sports equipment.
Further advantageous developments of the invention are described in the dependent claims.
Furthermore, these or other fillers also serve as crystallisation accelerators which are particularly useful for the generation of the crystalline state of the PET material, which is advantageous according to the invention.
While it is particularly preferable, according to the invention, to use a kneading unit having both a rotating and axially oscillating mixing screw, principally any mixing unit could be possible for the realization of the invention, which ensures a comparable mixing effectxe2x80x94homogenization while allowing water vapour to escape.
By means of the proved, particularly advantageous mechanical properties as well as by the PET material which can be made available at low cost and which has been hardly recyclable until now, a possibility has been shown according to the invention of how potential ecologically problematic materials can be used in an appropriate, technically efficient and advantageous way.
Even with amorphous PET which is used according to the invention, it is particularly advantageous that this material changes its structurexe2x80x94graduallyxe2x80x94towards the more tough crystalline PET under the influence of heat as, for example, when being used as a chimney-pipe.
An essential further development of the present invention is the processing of the crystalline PET produced and used according to the invention, by foaming, for example by means of a foaming agent, whereupon workpieces are formed which show a considerably lower specific gravity although their mechanical stability has been reduced insignificantly only. Furthermore, foaming agents show the advantageous effect that because of the gaseous foaming agent cooling-down of a formed product would be delayed thus further stimulating the generation of the crystalline state in the material. As an example for processing it is referred to the so-called integral foam injection.
Since PET is a generally long-chain polymer, it is especially in the case of injection moulding that a detail dissolution cannot be obtained in any amount because of the flow properties of the material. By adding appropriate additives, such as paraffins, stearins, wax or the like, to the liquid mixture, however, the friction both between the individual polymers (polymer chains) and between the latter and the moulding nozzles can be reduced considerably by the thus obtained wetting effect so that in particular for injection moulding processes or the like the working properties can be clearly improved.
According to the invention it is preferable to add a slip additive, such as sodium montanate in the amount of 0.1 to 3.0% by weight to the liquid PET, more preferably between 0.2 and 0.5% by weight.